Joking aside, the lifestyle is also different. Tokyo and HK where I live are known for tiny apartments, but they're also cities where residents spend far less time at home, offering cheap options for eating out, many places to hang out outside home, reliable transit, and extreme safety from crime at all times of the day. I'm far more comfortable in a tiny HK flat than I would be in the same size in SF. Thankfully I have the luxury of a decent sized space in both now.
Sadly you are correct about Japanese vs American sizing. But beyond that hanging clothes to dry vs having a dryer, inbuilt grills on stoves, rice cookers, dishwashers being rarer, etc all add up to more efficient use of space.
Joking aside, the lifestyle is also different. Tokyo and HK where I live are known for tiny apartments, but they're also cities where residents spend far less time at home, offering cheap options for eating out, many places to hang out outside home, reliable transit, and extreme safety from crime at all times of the day. I'm far more comfortable in a tiny HK flat than I would be in the same size in SF. Thankfully I have the luxury of a decent sized space in both now.